The cDNAs for human LDH-A and -B, and mouse LDH-A, -B and -C isozymes have been cloned and sequenced. Human LDH-A, -B and -C genes and pseudogenes have been mapped and isolated. The genomic structure of human LDH-A -B and -C genes as well as mouse LDH-A gene have been characterized. The protein-coding sequences of mammalian LDH-A, -B and -C genes are interrupted by six introns, and their relationships between protein structure and exon organization are illustrated. The developmental and tissue- specific expression of mouse LDH-A, -B and -C genes have been studied. The expression of mouse LDH-A gene was induced by cyclic AMP and estrogen. This information will allow more accurate evaluation of genetic mutation events caused by mutagens and eventually will be of value to improve human health care.